FIG. 1A is a schematic cross-sectional view of a conventional liquid crystal display panel. The liquid crystal display panel includes a first substrate 100, a second substrate 200 opposite to the first substrate 100, a material of liquid crystal (LC) 300 sealed between the first substrate 100 and the second substrate 200, and a backlight module (not shown) positioned back on the second substrate 200 to be served as a light source. A color filter 120 is disposed on internal surface of the first substrate 100 for providing each pixel with colors. Further, a layer of indium tin oxide (ITO) is coated on the color filter 120 and the internal surface of the first substrate 100 to serve as a common electrode 110. As shown in FIG. 1C, the second substrate 200 is a thin film transistor (TFT) array substrate. The internal surface of the thin film transistor array substrate includes a plurality of TFTs 230 at an array arrangement, a plurality of gate lines 12 at a horizontal arrangement, and a plurality of source lines 14 at a vertical arrangement. In FIGS. 1B and 1C, a TFT 230, a pixel electrode 220, a storage capacitor (Cs) 235, a LC capacitor (CLC) 240 form a unit pixel 250 near the intersection of each gate line 12 and each source line 14 and thus, a plurality of pixels are formed on the second substrate 200. The TFT 230 has a gate, a source, and a drain for electrically connecting to the gate line 12, the source line 14, and the pixel electrode 220, respectively. The storage capacitor (Cs) 235 consists of a common line 16, the pixel electrode 220 and a dielectric layer therebetween, while the LC capacitor (CLC) 240 consists of the common electrode 110, the pixel electrode 220 and the material of liquid crystal therebetween at the pixel. As shown FIG. 1C, the gate line 12, the source line 14 and the common line 16 on the second substrate 200, respectively, extend from a pixel display area 256 to a periphery area 258 for connecting to each of the bonding pads 20 correspondingly and inputting a control signal or a control voltage via the bonding pads 20. The gate line 12 and the source line 14 are electrically connected to a scan driving circuit (or scan driving chip) 260 and a data driving circuit (or a data driving chip) 280, respectively, via the bonding pad 20. Furthermore, the scan driving circuit 260 and the data driving circuit 280 are positioned on the periphery area 258 outside the pixel display area 256 of the TFT array substrate 200. In one embodiment, the common line 16 is in a ground connection. In another case, an external voltage is inputted to the common line 16 via the bonding pad 20.
When the scan driving circuit 260 outputs a pulse signal to the gates of the TFTs 230 via the bonding pad 20 and the gate line 12, the TFTs 230 turn on for writing the data signal of the source line 14 to the LC capacitor (CLC) 240 and the storage capacitor (Cs) 235 via the gates and drains of the TFTs 230. Then, an electric field between the common electrode 110 and the pixel electrode 220 is generated for controlling the twist direction of the liquid crystal molecules in a material of liquid crystal 300 so that the light emitted from the backlight module penetrates the liquid crystal molecules and a pixel color is thus formed on the first substrate 100, as shown in FIG. 1A. Conversely, when the pulse signal is in off-state, the TFTs 230 turn off so that the data written into the LC capacitor (CLC) 240 and the storage capacitor (Cs) 235 are kept invariant. That is, the display signal is kept in constant on the pixel 250 so that each pixel 250 serves as the function of memorization until the pulse signal is in on-state.
Based on the alignment process, the twist angle and the driving method of the liquid crystal, the LCD is usually classified into a twisted nematic (TN) type, a super twisted nematic (STN) type, and a thin film transistor (TFT) type. The full color of LCD which is applicable to some of the electronic devices, such as computer, adopts the thin film transistor (TFT) type, e.g. active matrix thin film transistor liquid crystal display.
For the purpose of controlling the display efficiency during the conventional display process, it is required to perform an alignment process on the TFT array substrate and the color filter substrate of the LCD for forming an alignment layer in order to conduct the liquid crystal molecules between the top and bottom substrates along a specific direction and generate a pre-tilt angle. For example, during the process of polymer-dispersed liquid crystal, a polymer-induced phase separation (PIPS) technique is utilized. The PISP technique includes the following steps: (1) mixing the photo-polymerizable monomers with the liquid crystal at a predetermined ratio and then sealing the mixed material to be positioned between the top and bottom substrates for forming a predetermined thickness of liquid crystal cells; (2) when UV light irradiates on one side of the liquid crystal cells, the polymerization occurs and then a polymer film is formed near the surfaces of the liquid crystal cells on which the UV light illuminates. Further, when the liquid crystal separates from the polymer, the liquid crystal is far away from the surfaces of the liquid crystal cells on which the UV light illuminates and moves to the center of the liquid crystal cells, which is named as phase separation effect. Since the alignment layer between the top and bottom substrates is capable of orientating liquid crystal molecules, the aligned liquid crystal molecules are generated based on the function of the alignment layer. Such a process of alignment layer has the same function and better alignment as to the conventional process of the alignment of the liquid crystal, such as a rubbing step, a photo-alignment step and a photo-sensitive step.
FIG. 2A shows another case of PSA process. Some photocurable monomers 310 are mixed with the material of liquid crystal (LC) 300 and the mixed material is sealed between the top and bottom substrates to form the predetermined thickness of liquid crystal cells 30. Furthermore, each the internal surface of the liquid crystal cells 30 near the top and bottom substrates has a polyimide (PI) layer 306 (not clearly shown), made by such as a rubbing step. Afterwards, as shown in FIG. 2B, when a low level curing voltage is applied on the electrodes of the top and bottom substrates for generating an electric filed (E) between the top and bottom substrates in order to control liquid crystal molecules in the material of liquid crystal (LC) 300 tilted at a predetermined direction. However, the electric filed (E) does not exert the force on the monomers 310, thereby generate a phase separation status. As shown in FIG. 2C, when the curing voltage is exerted, the UV light irradiates the liquid crystal cells for curing the monomers 310 by polymerization to respectively form a polymer layer 312 on the internal surfaces of the top and bottom substrates. As shown in FIG. 2D, when the curing voltage is dispersed to vanish the electric field, the function of polymer layers 312 on the internal surfaces of the top and bottom substrates is similar to the function of a conventional alignment layer. That is, based on the arrangement direction of the polymer in the polymer layer 312, the liquid crystal molecules (LC) 300 of the liquid crystal cells 30 tilt at a pre-tilt angle. If the alignment for the liquid crystal molecules is invalid, the refraction direction of the light is incorrect, thereby resulting in incorrect display of the LCD.